Process and device for operating a rain sensor

ABSTRACT

An apparatus and a method for operating a rain sensor ( 10 ) that outputs a sensor signal ( 18, 22 ) as a function of the wetting of a window ( 11 ) are proposed, having a controller ( 16 ) which as a function of the sensor signal ( 18, 22 ) outputs a control signal ( 28 ) to the rain sensor ( 10 ) for regulating the sensor signal ( 18, 22 ); for signal evaluation, the sensor signal ( 18, 22 ) and in addition the control signal ( 28 ) are used for tripping switching events of a device.

PRIOR ART

[0001] The invention is based on an apparatus and a method for operatinga rain sensor as generically defined by the preamble to the main claim.

[0002] From German published, nonexamined Patent Application DE-OS 41 12847, an apparatus for operating a rain sensor is already known having atransmitter which is triggered by a preceding control arrangement, areceiver which outputs a sensor signal to a signal processor, and anevaluator, which outputs a switching signal for turning a windshieldwiper on as a function of the sensor signal.

[0003] A regulator is also provided that regulates the sensor signal,which corresponds to a clean window, to a predetermined resting level.To that end, the controller outputs a control signal to the controlarrangement of the transmitter for the sake of slowly regulating thetransmission power to a predetermined resting level. Alternatively, thecontroller outputs a control signal to the signal processor for slowlyregulating the gain of the sensor signal to be amplified. With theregulator, production variations among individual components of the rainsensor as well as tolerances in rain sensor installation can becompensated for over a wide range.

[0004] A disadvantage is that the controller regulates the sensor signalcorresponding to a clean, dry window to the resting level, preferably atthe outset, and that over the further course of sensor operation thecontrol signal of the controller is allowed to vary in comparison withthe sensor signal only extremely slowly, so that changes in the sensorsignal will not be cancelled out. That is, the regulator essentiallyperforms a (one-time) calibration of the rain sensor.

[0005] This then means that the evaluation of the sensor signal takesplace essentially in the working range that has been set. This has thedisadvantage that at small sensor signals, any change in the sensorsignal has poorer resolution than an equally major relative change inlarge sensor signals.

ADVANTAGES OF THE INVENTION

[0006] The apparatus according to the invention having thecharacteristics of the body of the main claim has the advantage that acontroller regulates a rain sensor as a function of the degree ofwetting of a window, and that the sensor signal and in addition thecontrol signal of the controller are delivered to an evaluationarrangement for evaluation. In this way, the control signal and theworking range can be tracked directly and quickly as a function of thesensor signal, without the sensor signal being cancelled out. Theworking range of the sensor signal can therefore be selected to besmaller, so that for a suitable gain the resolution becomes greater.

[0007] With the provisions recited in the dependent claims, advantageousrefinements of and improvements to the characteristics recited in themain claim are obtained. One particular advantage is the spatialseparation of the evaluation arrangement from the control circuit forthe rain sensor, which is made possible by the fact that the regulationis performed by an electronic regulator, so that a microcontroller isused only for the evaluation.

[0008] As a further advantage, the evaluation arrangement ormicrocontroller is there for part of a central electronic system of amotor vehicle.

[0009] It is also advantageous that the microcontroller requires onlylow power and a low clock speed, because as a “listener”, it merelyevaluates signals.

[0010] Another advantage is that the controller regulates the workingrange of the transmitter continuously or in stages and is embodied in aspace-saving way as an ASIC (application-specific IC).

[0011] The separate transmission of the sensor signal and the controlsignal to the microcontroller is especially advantageous. As a result, awide dynamic scope of the microcontroller input and high resolution areobtained. A further advantage is the use of a differential amplifier toevaluate the sensor signal. This sets a differential working range, sothat slight signal changes can be evaluated with high resolution in theevaluation arrangement.

DRAWING

[0012] Exemplary embodiments of the invention are shown in the drawingand described in further detail in the ensuing description.

[0013]FIG. 1 shows a schematic circuit diagram of a control circuit of arain sensor;

[0014]FIG. 2 shows a circuit for evaluating control signals and sensorsignals; and

[0015]FIG. 3 shows an alternative exemplary embodiment of a circuitdiagram of a control circuit.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0016]FIG. 1 shows a rain sensor 10, which has at least one transmitter12 and one receiver 14 and is operated in a control circuit with acontroller 16. The rain sensor detects the wetting of a motor vehiclewindow 11, for instance, by moisture and is disposed in the wiping areaof a windshield wiper (not shown).

[0017] The rain sensor 10 functions on an optoelectronic principle.However, some other sensor principle is equally suitable. For instance,acoustic, capacitive and resistive rain sensors are known. The acousticrain sensor converts sound waves into a corresponding electrical outputsignal; the resistive rain sensor varies its conductance, and thecapacitive rain sensor varies its capacitance upon the occurrence ofmoisture or dirt on the window.

[0018] The optoelectronic rain sensor 10 used here includes alight-emitting transmitter 12, whose light is coupled into the window11, passed through the window 11, and out-coupled at a certain point ofthe window 11 to a light-detecting receiver 14. The receiver 14 convertsthe detected light quantity into a sensor signal 18, which is deliveredto a signal processor 20. The signal processor 20 is embodied as anoperational amplifier. The use of other current-voltage converters isalso possible, however. The signal processor 20 is located in the rainsensor 10, but may also be disposed outside the rain sensor 10.

[0019] The processed sensor signal 22 (22.1) is delivered on the onehand to the analog controller 16 of the control circuit, which regulatesthe transmitter current 27 of the transmitter 12 as a function of thesensor signal 22. To that end, the controller 16 outputs a controlsignal 28 (28.1), with which a capacitor is charged, whose capacitorvoltage acts as a control voltage for a voltage-controlled currentsource 26. A comparator is integrated with the controller 16 andcompares the level of the sensor signal 22 with limit values of apredetermined working range. As a function of the outcome of thecomparison, the control signal 28 is increased, decreased, or keptconstant. The controller 16 of the control circuit is also disposed in aspace-saving manner as an ASIC in a housing of the rain sensor 10, whichhousing is mounted on the window 11 of the motor vehicle.

[0020] The sensor signal 22 (22.2) is delivered on the other hand to acircuit according to FIG. 2 for evaluation; this circuit includes, amongother elements, a differential amplifier 30, an analog/digital converter32, and an evaluation arrangement 34.

[0021] According to the invention, the control signal 28 (28.2) of thecontroller 16 is also delivered to the evaluation arrangement 34, via asecond A/D converter 36.

[0022] If a microcontroller is used for evaluating the signals 22, 28,then the A/D converters 32, 36 are typically integrated with themicrocontroller. In the case of analog evaluation, the A/D converters32, 26 can be dispensed with.

[0023] Via an output signal 40 of the evaluation arrangement 34, adownstream apparatus, such as a wiper motor 42 of a motor vehiclewindshield wiper system, is triggered automatically as a function of thewetting of the window.

[0024] The evaluation circuit of FIG. 2 is part of a central electronicsystem of the motor vehicle, but it can also be disposed on the wipermotor 42 or in the rain sensor housing.

[0025] The mode of operation of the apparatus of the invention as shownin FIGS. 1 and 2 will now be described in further detail.

[0026] First, the control circuit should be explained. The receiver 14outputs a sensor signal 18 to the signal processor 20, and this signalis amplified there in such a way that the maximum value for the sensorsignal 22 is at 5 volts, for instance. The amplification is effectedlinearly. In the controller 16, the range between 4 and 5 volts isspecified as the working range for the sensor signal 22. The signal 22delivered to the controller 16 is compared by the comparator with thetwo limit values of the working range.

[0027] If the sensor signal 22 is between the two limit values, then thecontrol signal 28, by way of which the transmitter power is triggered,remains unchanged. As already described at the outset, the input voltageof the voltage-controlled current source 26 is defined by the controlsignal 28. Thus the current 27 generated by the current source 26, andhence also the transmitter power of the transmitter 12, are specified asa function of the control signal 28.

[0028] If the sensor signal 22 is below the lower limit value, then thecontroller 16 outputs a rising control signal 28, and thus also anincrease in current 27, until the sensor signal 18, 22 output by thereceiver 14 is again within the working range of the comparator.

[0029] In the opposite case, if the sensor signal 22 exceeds the upperlimit value, the controller 26 reduces the control signal 28 and thusalso the current 27 and the transmission power. The control signal 28 isreduced until such time as the sensor signal 22 is again within theworking range.

[0030] Independently of the mode of operation of the control circuit ofFIG. 1, sensor signals 22 (22.2) and control signals 28 (28.2) are alsodelivered to the evaluation arrangement 34. The linearly amplifiedsensor signal 22 is delivered to the differential amplifier 30, whichextends the working range. The maximum sensor signal 22 is applied tothe maximum input of the microcontroller. For an 8-bit microcontrollerand a maximum sensor signal of approximately 5 volts, one bitcorresponds to approximately 20 millivolts. Because on account of thedefined working range of the controller 16 only high levels of thesensor signal 22 are evaluated, very good resolution is obtained.

[0031] The evaluation of the sensor signals 22 and control signals 28 inthe evaluation arrangement 34 or microcontroller is now done as follows:

[0032] As long as the control signal 28 remains constant, the evaluationarrangement 34 evaluates only the sensor signal 22 for the wetting of awindow by rain, moisture, ice or dirt and by means of output signals 40triggers a windshield wiper system with a wiper motor 42. Thresholds arestored in memory for this purpose in the evaluation arrangement 34. Whena first threshold is reached by the sensor signal 22, one wiper mode(intermittent or constant operation) is typically tripped.

[0033] If the sensor signal 22 moves out of the working range, thisrequires correction of the transmitter power of the transmitter 12 byincreasing or decreasing the control signal 28, which is done by thecontroller 16. The evaluation arrangement 34 detects the change in thecontrol signal 28 and then evaluates only the control signal 28 with aview to triggering the wiper motor 42. The sensor signals 22 are nottaken into account then. Once the control signal 28 reaches a furtherthreshold, stored in the evaluation arrangement 34, a wiper mode istripped.

[0034] As soon as the sensor signal 22 is again within the workingrange, the control signal 28 remains constant. This is detected by theevaluation arrangement 34, and after that only the sensor signal 22,instead of the control signal 28, is taken into account for theevaluation.

[0035]FIG. 3 shows an alternative exemplary embodiment of the controlcircuit, in which the controller 16 acts on the signal processor 20 ofthe sensor signal 18. By varying the gain for the sensor signal 18 inthe signal processor 20, the amplified sensor signal 22 is regulatedinto the working range. The transmission power of the transmitter 12 isthus set to be constant, and near a maximum value, by the current source26. The evaluation of the sensor signal 22 (22.2) and the control signal28 (28.2) is done analogously to the evaluation described above.

[0036] In a modification of the exemplary embodiments of FIGS. 1 through3, a digital controller 16 is used, which outputs control signals 28 tothe voltage-controlled current source 26 as a function of digital sensorsignals 22. The regulation takes place here via a resistor circuit inthe controller 16, so that discrete control signals 28 allow regulationof the transmitter power of the transmitter 12 in stages. The A/Dconverters 32/36 in the evaluation arrangement of FIG. 2 are omitted.

1. An apparatus for operating a rain sensor (10) which is used forautomatic triggering of a device, in particular a windshield wiper formotor vehicles, having a transmitter (12), a receiver (14) whose sensorsignal (18) is delivered to a signal processor (20) and to an evaluationarrangement (34) downstream thereof, and a controller (16), which as afunction of the sensor signal (18, 22) outputs a control signal (28) tothe rain sensor (10) for regulating the sensor signal (18, 22),characterized in that in addition to the sensor signal (18, 22), thecontrol signal (28) is also delivered to the evaluation arrangement (34)for tripping switching events of the device.
 2. The apparatus of claim 1, characterized in that the evaluation arrangement (34) is disposedspatially remotely from the rain sensor (10) and/or the controller (16),and preferably forms part of a central electronic system of a motorvehicle.
 3. The apparatus of claim 1 , characterized in that thecontroller (16) regulates the transmission power of the transmitter (12)continuously or in stages, in particular upon attainment of limit valuesfor the working range of the rain sensor.
 4. The apparatus of claim 1 ,characterized in that the controller (16) is constructed as an ASIC(application-specific IC).
 5. The apparatus of claim 1 , characterizedin that it has a differential amplifier 30 for amplifying the sensorsignal
 22. 6. The apparatus of claim 1 , characterized in that thecontrol signals 28 or sensor signals 18, 22 delivered to the evaluationarrangement 34 are analog or digital.
 7. The apparatus of claim 1 ,characterized in that it is intended for use for triggering a wipermotor (42) of a windshield wiper system.
 8. A method for operating arain sensor (10) which is used for automatic triggering of a device, inparticular a windshield wiper for motor vehicles, having a transmitter(12), a receiver (14) whose sensor signal (18) is delivered to a signalprocessor (20) and to an evaluation arrangement (34) downstream thereof,and a controller (16), which as a function of the sensor signal (18, 22)outputs a control signal (28) to the rain sensor (10) for regulating thesensor signal (18, 22), characterized in that in addition to the sensorsignal (18, 22), the control signal (28) is also delivered to theevaluation arrangement (34) for tripping switching events of the device.9. The method of claim 8 , characterized in that the evaluationarrangement (34) evaluates the control signal (28) and/or the sensorsignal (18, 22).
 10. The method of claim 8 , characterized in that theevaluation arrangement (34) evaluates the sensor signal (18, 22) if thecontrol signal (28) is constant, and if the control signal (28) isvarying, it evaluates the control signal (28) independently of thesensor signal (18, 22) for tripping switching events of the device.